The present invention relates to a gas turbine engine having a two-stage combustion changing system capable of changing the fuel combustion mode from diffuse combustion to premixed combustion and reverse in accord with its load conditions.
Typically, gas turbine engines of this type adopt two-stage combustion changing system that conducts diffuse combustion by feeding only fuel through a first inject nozzle into a combustion chamber (burner) to improve ignition and/or flame stability at the engine starting time or with a decreased load and conducts premixed combustion by feeding fuel premixed at a specified air-fuel ratio through a second injection nozzle into the combustion chamber to improve emission efficiency at a normal load.
In applying the two-stage combustion changing system, there arises such a problem that, when switching the combustion mode, temporal changes in rotation speed of the engine occur because a delay in feeding fuel occurs due to the capacity of a fuel gallery of a fuel-supply-side nozzle-line and fuel remaining in a fuel galley of a fuel-supply cutoff nozzle-line is purged together with air into the combustion chamber when conducting air-purging for preventing nozzle caulking in the nozzle.
The variation in rotation speed (the number of revolutions per minute) of the engine when changing the combustion mode can be prevented by shortening the length of the fuel gallery of each nozzle line to reduce the capacity of the gallery. However, it is very difficult to reduce the capacity of the gallery in practice because of severe limitations on layout of the fuel lines and nozzles, which must not be placed in the places where high heat radiation may arise. Actually, the variation in the rotation speed has not sufficiently been reduced.
The problem to be solved is such that a gas turbine with two-stage combustion changing system varies its rotation speed when changing the combustion mode because a delay in feeding fuel occurs due to the capacity of a fuel gallery of the fuel-supply-side nozzle-line and fuel remaining in a galley of a fuel-supply cutoff nozzle-line is purged together with air into the combustion chamber at the time of air-purging for preventing the nozzle from be caulked.
Accordingly, an object of the present invention is to provide a gas turbine engine having a two-stage combustion changing system that can change two combustion stages from the diffuse combustion to the premixed combustion and vice versa, effectively preventing the changes in engine rotation speed by using a means for carrying-out air-purging of a nozzle on the fuel-supply shutoff line simultaneously with changing a current combustion stage to the other and a means for restricting a fuel flow rate to a nozzle on a fuel-supply nozzle-line for a certain period.